Battery comprising ink

ABSTRACT

In one aspect, a method of making a battery includes fusing an alkali metal onto a patterned conductive layer. In another aspect, a method of forming a battery includes: a) providing a cathode base which comprises: a first nonconductive surface; a first conductive layer superjacent the first nonconductive surface; the first conductive layer comprising a first area; and a cathode layer superjacent the first conductive layer leaving at least a portion of the first area exposed; b) providing an anode base which comprises: a second nonconductive surface; a second conductive layer superjacent the first nonconductive surface, the second conductive layer comprising a second area; and an anode layer superjacent the second conductive layer leaving at least a portion of the second area exposed, the anode layer comprising an alkali metal; and c) aligning and coupling the anode layer of the anode base with the cathode layer of the cathode base, wherein the aligning and coupling leaves at least a portion of the first area and at least a portion of the second area exposed for electrical connection. The invention also encompasses batteries formed by such methods.

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patentapplication Ser. No. 08/842,550, filed Apr. 15, 1997, U.S. Pat. No.5,747,191, which is a divisional application of U.S. patent applicationSer. No. 08/645,614, filed on May 14, 1996, now U.S. Pat. No. 5,735,912,entitled "Battery Constructions And Method For Forming Such BatteryConstructions", listing the inventor as Rickie C. Lake, which is acontinuation-in-part of U.S. patent application Ser. No. 08/071,463,filed Jun. 2, 1993, which is now issued U.S. Pat. No. 5,624,468.

TECHNICAL FIELD

The present invention relates generally to a process for forming abattery and to batteries.

BACKGROUND OF THE INVENTION

Advancements in semiconductor technology have led to the production oflarge scale integrated circuits which have revolutionized theelectronics industry. Microelectronic components are now widely used inthe production of a variety of electronic devices, such as portablecomputers, calculators, watches, cordless telephones, radios, taperecorders, and security systems. Development of such electronic deviceshas brought about the evolution of batteries as miniature powersupplies. In light of their applications, this new generation ofbatteries must produce higher energy per unit volume and superiordischarge characteristics.

The technology related to thin solid state batteries has been developingat a rapid pace. Thin solid state batteries are typically fabricatedemploying an alkali metal anode, a non-aqueous electrolyte, and cathodesof nonstoichiometric compounds, such as teachings of U.S. Pat. Nos.4,621,035; 4,888,206; 4,911,995; 5,169,446 and U.S. Pat. No. 5,080,932.Of the alkali metals commercially feasible in manufacturing the anodematerial, lithium is preferred because it has a low atomic weight, whilehaving a high electronegativity. These thin batteries require a highenergy density, a long shelf life and efficient operation over a widerange of temperatures.

One known method for fabricating a thin battery cell is shown in FIGS.1(A-G). Referring to FIG. 1(A), a current collector film 110 isinitially provided. Collector film 110 can comprise a variety ofconductive materials, including but not limited to stainless steel,copper, nickel or aluminum. Subsequently, as shown in FIG. 1(B), acathode layer 112 is positioned superjacent the current collector film,preferably by extrusion. This step also involves curing to sufficientlypolymerize the cathode. Referring to FIG. 1(C), after the cathode layeris cured, an electrolyte layer 114 is positioned superjacent the cathodeand subsequently cured, thereby forming currentcollector-cathode-electrolyte sandwich 115. Next, from the currentcollector-cathode-electrolyte sandwich 115, a multitude of subsections116 are formed, as shown in FIG. 1(D). Then, each subsection 116 has ananode foil 118 comprising lithium or some other suitable alkalipositioned superjacent, as illustrated in FIG. 1(E). Referring to FIG.1(F), a second conductive layer 120 is then subsequently positionedsuperjacent the anode foil 118.

Referring to FIG. 1(G), each subsection 116 is then packaged in astainless steel enclosure 122 such that one current collector is inelectrical contact with the top portion 124 of the stainless steelenclosure and the other collector is in contact with the bottom portion126 of the enclosure. To ensure against potential shorting, insulation128 is positioned within the enclosure between the top and bottomportions of the stainless steel enclosure.

Previously, thin battery manufacturing technology has relied on formingand assembling the anode, electrolyte, and cathode of the battery asseparate components. However, this is a relatively labor intensiveprocedure that involves the intricate assembly of a number of discretecomponents. The stamping and handling of individual discs of lithium isparticularly costly and awkward because of lithium's expense andrelatively high reactivity. Thin lithium foil is also difficult to workwith. Thin lithium foil comprises malleable, low tensile strengthproperties. Moreover, lithium foil adheres to a large number of othermaterials.

In light of these shortcomings, there have been several developments inthe manufacturing processes of thin battery technology. Theseadvancements, such as U.S. Pat. No. 4,911,995, and U.S. Pat. No.4,621,035, have relied on the utilization of a thin metal film as ametalization layer. This metalization layer is then employed with analkali metal to form an anode. However, these approaches fail to providea battery which has the flexibility and durability required in someelectronics applications, as well as a simplified means formanufacturing.

Polymer thick film inks have yet to be examined as a conductive layerfrom which a lithium anode may be formed. Many of the difficulties inmanufacturing polymer batteries are related to handling and assemblingthe lithium anodes, the cathodic polymers and the electrolytic polymers.These issues are compounded in part because most techniques known in theart for fabricating these battery types involve forming one battery cellat a time.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1(A)-(G) are planar cut-away views of a prior art method forfabricating a battery cell.

FIG. 2(A)-(F) are planar cut-away views of a first base undergoing stepsof the present invention.

FIG. 3(A)-(E) are planar cut-away views of a second base undergoingsteps of the present invention.

FIG. 4 is a three dimensional cut-away view of both the first and secondbases prior to assembly of a battery cell.

FIG. 5 is a three dimensional view of a battery cell produced by amethod of the present invention.

It is emphasized that the drawings of the instant application are merelyschematic representations and are not intended to portray the specificparameters of the structural details of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In accordance with one aspect of the invention, a method of making abattery comprises the step of fusing an alkali metal onto a patternedconductive layer.

In accordance with another aspect of the invention, a method of forminga battery comprises:

providing a cathode base, the cathode base comprising:

a first nonconductive surface;

a first conductive layer superjacent the first nonconductive surface;

the first conductive layer comprising a first area; and

a cathode layer superjacent the first conductive layer leaving at leasta portion of the first area exposed;

providing an anode base, the anode base comprising:

a second nonconductive surface;

a second conductive layer superjacent the first nonconductive surface,the second conductive layer comprising a second area; and an anode layersuperjacent the second conductive layer leaving at least a portion ofthe second area exposed, the anode layer comprising an alkali metal; and

aligning and coupling the anode layer of the anode base with the cathodelayer of the cathode base, wherein the aligning and coupling leaves atleast a portion of the first area and at least a portion of the secondarea exposed for electrical connection. In accordance with anotheraspect of the invention, a battery comprises:

a first nonconductive layer;

a first conductive layer against the first nonconductive layer;

a cathode against the first conductive layer;

a second nonconductive layer;

a second conductive layer against the second nonconductive layer, thesecond conductive layer comprising a cured conductive ink; and

an alkali metal fused to the second conductive layer. More specifically,the present invention encompasses formation of a cathode base and ananode base, and the subsequent coupling of these bases to form abattery. The present invention also encompasses batteries formed by sucha method.

The formation of a cathode base in accordance with the present inventionis described with reference to FIG. 2(A-F).

Referring to FIG. 2(A), a nonconductive first base 10 is provided. Asshown, first base 10 has an upper surface 11. First base 10 ispreferably an electrically insulating (nonconductive) film andpreferably comprises polyimide. A polyimide film which has been found tobe suitable for the present invention is sold under the trademark KAPTONfrom Dupont. Polyester, glass, ceramics, or other polymer films may alsobe employed as materials in the construction of first base 10.Optimally, first base 10 is an elastic material. This will help tocreate a flexible battery.

Referring to FIG. 2(B), one or more first voids or slots 15 are providedwithin first base 10. Slots 15 provide electrical access to aneventually formed anode, as described below with reference to FIGS. 4and 5. Slots 15 may be punched out of base 10, or formed duringextrusion of base 10, or formed by alternate methods known to persons ofordinary skill in the art.

Referring to FIG. 2(C), a first conductive layer 20 is providedsuperjacent first base 10 and aligned with first slots 15. Preferably,conductive layer 20 is applied to base 10 to form a pattern which coversonly a portion of upper surface 11 and which has a plurality ofsubstantially identical repeating units 21 aligned in a one-to-onecorrespondence with each slot of the plurality of slots 15. Firstconductive layer 20 serves the same functional purposes as the currentcollector of the known art. However, because its formation employsconductive ink technologies, it provides much greater flexibility. Firstconductive layer 20 preferably comprises conductive polymer thick filmink. However, the conductive layer 20 may instead comprise standardthick film ink or high temperature thick film ink. Standard and thickfilm inks are generally fixed at relatively high temperatures, above800° C., and are therefore generally most suitable for bases comprisingmaterials with high temperature stability, such materials includingceramics and glass.

Alternatively conductive layer 20 may be provided as a metallic layersuperjacent first base 10. One method for forming such a metallic layeris to start with an insulative film having a layer of metal across it'ssurface. The metallic layer is then etched to form the second conductivelayer 20, in a pattern comprising the repeating unit 21, over a firstbase 10 comprising the insulative film. The starting insulative filmwith a layer of metal on it's surface can be made by several methodsknown to persons of skill in the art, such as by vapor depositing,sputter depositing, or adhesively adhering a metal onto a polyimide orpolyester sheet. The starting insulative film with a layer of metal onit's surface can also be purchased. One such purchased film which hasbeen found to be satisfactory for the present invention is sold a scopper-clad KAPTON by Dupont.

If first conductive layer 20 is formed from a ink, the provision ofconductive layer 20 preferably involves two independent steps. First,the ink, in liquid form, is printed directly superjacent first base 10.Second, the ink is cured to form layer 20. The curing step can beaccomplished through a variety of means, including exposing the ink toenergy in one or more of the forms of heat, ultraviolet light, infraredlight, or electron beam energy. The choice of the form of energy may bevaried depending on the type of ink selected. The temperature employedin order to complete the step of curing varies depending on the lengthof heating, as well as the thickness of the film. Example conditions forcuring a polymer thick film ink are from about 130° C. to about 165° C.for approximately 60 seconds to approximately 30 minutes.

If conductive layer 20 is formed from a metallic layer, it may beprovided by methods identical to those discussed below regarding theapplication of a second conductive layer 60 (shown in FIG. 3C) to asecond base 50 (shown in FIG. 3C).

In the shown embodiment of the present invention, first conductive layer20 is in electrical contact with a first conductive pad area 25.Preferably, pad area 25 is applied simultaneously with layer 20.However, first conductive pad 25 may also be applied before or afterfirst conductive layer 20 is provided, such as by printing pad 25 afterprovision of layer 20. As discussed below with reference to FIGS. 4 and5, conductive pad area 25 forms a cathode contact 27 for electricalconnection to the cathode of the finally formed battery 95 (shown inFIG. 5).

Referring to FIG. 2(D), first conductive pad 25 may be covered by acapped tip 28. Tip 28 is preferably formed by printing a carbon basedpolymer thick film ink directly onto a portion of first conductive pad25 and curing the combination using the techniques described aboveregarding the curing of layer 20. Capped tip 28 increases the wearresistance and durability of cathode contact 27.

Referring to FIG. 2(E), a cathode layer 30 is provided superjacent firstconductive layer 20. Cathode layer 30 may be provided as a conductiveliquid or paste. In a less preferred embodiment, cathode layer 20 mayalso be provided as a conductive solid.

The cathode material selected will generally comprise one or more ofmanganese, cobalt, MnO₂, V₂ O₅ or V₆ O₁₃. Cathode layer 30 may alsocomprise other materials known to persons of ordinary skill in the art.

If cathode layer 30 is provided as a liquid or paste, the provisionpreferably comprises the following two steps. First, the material ofcathode layer 30, in liquid form, is applied superjacent firstconductive layer 20. Most preferably, this application is accomplishedby screen, stencil or pad printing the liquid onto layer 20. Second, thematerial of cathode layer 30 is cured. The curing step may beaccomplished using the techniques described above regarding the curingof first conductive layer 20.

If the cathode layer 30 is provided as a solid, a conductive epoxy resinmay be provided between cathode layer 30 and first conductive layer 20to help adhere cathode layer 30 to conductive layer 20.

Provision of cathode layer 30 over conductive layer 20 completesformation of a cathode base 31. The individual cathode bases 31 can nextbe cut-away and separated from one another. In a less preferredembodiment of the invention, which has not been shown, only oneindividual cathode base 31 is patterned onto the insulative base 10. Insuch a less preferred embodiment there is no need to cut and separateindividual cathode bases.

Referring to FIG. 2(F), an electrolyte film 40 may be providedsuperjacent cathode 30 before the individual cathode bases 31 arecut-away and separated from one another. Electrolyte film 40 preferablycomprises a liquid or paste, and is most preferably screen or stencilprinted onto cathode layer 30 and not onto the uncovered surfaces ofsurface 11 (surface 11 is described with reference to FIG. 2A).Provision of electrolyte film 40 preferably comprises two steps. First,electrolyte film 40, in the liquid or paste form, is applied superjacentcathode layer 30. Second, electrolyte film 40 is cured. The curing stepmay be accomplished using the techniques described above regarding thecuring of layer 20. Although a preferred method for applying electrolytefilm 40 is described, known methods for applying electrolyte film, suchas the placement of a sheet of electrolyte film superjacent cathodelayer 30, may also be employed with the method of the present invention.Also, although electrolyte film 40 is shown provided with cathode base31, the electrolyte film may also be provided with an anode base 71(described below), or as a film which is separate from both the anodebase and the cathode base prior to the final battery 95 (shown in FIG.5) being formed.

The formation of an anode base in accordance with the present inventionis described with reference to FIGS. 3(A-E).

Referring to FIG. 3(A), a nonconductive second base 50 is shown. Asshown, second base 50 has an upper surface 53. Second base 50 ispreferably an electrically insulating (nonconductive) film, andpreferably comprises polyimide. A suitable polyimide film for theprocess of the present invention is sold under the trademark KAPTON fromDupont. Polyester, glass, ceramics or other polymer films may also beemployed in the construction of base 50. Preferably, second base 50,like the above-discussed first base 10, is a very elastic material.

Referring to FIG. 3(B), one or more second voids, or slots, 55 areprovided within second base 50. Slots 55 provide electrical access tocathode layer 30, as described below with reference to FIGS. 4 and 5.Slots 55 are preferably punched out or extruded from second base 50, butmay be formed by alternate methods known to persons of ordinary skill inthe art.

Referring to FIG. 3(C), a second conductive layer 60 is providedsuperjacent second base 50 and aligned with second slots 55. Secondconductive layer 60 preferably comprises either a conductive polymerthick film ink or a metallic layer. Like the conductive layer 20,discussed above, conductive layer 60 may also be formed from standardthick film ink or from high temperature thick film ink.

Preferably, conductive layer 60 forms a pattern over second base 50which covers only a portion of upper surface 53 and which has aplurality of substantially identical repeating units 61 aligned in aone-to-one correspondence with each slot of the plurality of slots.

A preferable procedure for providing second conductive layer 60superjacent second base 50 involves applying a liquid conductive polymerthick film ink onto the second base 50. Such conductive polymer thickfilm inks typically comprise electrically conductive metallic flecks,such as flecks of silver or copper. In this preferable procedure, theconductive polymer thick film ink, in a liquid form, is applied directlysuperjacent second base 50 in a pattern comprising the repeating unit61. The liquid ink is preferably applied by a printing method, such aspad printing or stencil printing. After the ink is applied, it is curedto form the second conductive layer 60. The curing step can beaccomplished using the techniques described above regarding the curingof layer 20.

An alternate procedure for providing second conductive layer 60superjacent second base 50 involves forming a metallic layer on base 50.One method for forming such a metallic layer is to start with aninsulative film having a layer of metal across it's surface. Themetallic layer is then etched to form the second conductive layer 60, ina pattern comprising the repeating unit 61, over a second base 50comprising the insulative film. The starting insulative film with alayer of metal on it's surface can be made by several methods known topersons of skill in the art, such as by vapor depositing, sputterdepositing, or adhesively adhering a metal onto a polyimide or polyestersheet. The starting insulative film with a layer of metal on it'ssurface can also be purchased. One such purchased film which has beenfound to be satisfactory for the present invention is sold ascopper-clad KAPTON by Dupont.

In some embodiments of the invention, the layer 60, once formed, isplated. Such plating may provide a better metallic surface for thefusing of an alkali metal which occurs in later steps of the invention.The plating may be accomplished by either electrolytic or electrolessmethods. If the conductive layer 60 which is to be plated has beenformed from a thick film ink, the thick film ink will preferably be aplateable thick film ink. An example plateable thick film ink which hasbeen found to work for the process of the present invention is plateableelectrically conductive ink, Number 117-31, sold by Creative MaterialsIncorporated, located in Tyngsboro, Mass.

In the shown embodiment of the present invention, second conductivelayer 60 is in electrical contact with a second conductive pad area 65.Pad area 65 is generally formed by the same methods used to formconductive layer 60. Preferably, pad area 65 is provided simultaneouslywith layer 60. However, second conductive pad 65 may also be providedbefore or after second conductive layer 60, such as by printing pad area65 after the provision of layer 60. As discussed below with reference toFIGS. 4 and 5, pad area 65 forms an anode contact 67 for electricalconnection to the anode of the finally formed battery.

Referring to FIG. 3(D), second conductive pad 65 may be covered by acapped tip 68. Tip 68 is preferably formed by printing a carbon basedpolymer thick film ink directly onto a portion of second conductive pad65 and curing the combination using the techniques described aboveregarding the curing of layer 20. Capped tip 68 increases the wearresistance and durability of anode contact 67.

Referring to FIG. 3(E), an anode layer 70 is provided superjacent secondconductive layer 60. An ode layer 70 comprises an alkali metal,preferably lithium. Anode layer 70 is preferably provided overconductive layer 60 by a wave-soldering-like method in which the base 50and conductive layer 60 is inverted over a molten "wave" of the alkalimetal. The alkali metal then contacts conductive layer 60 and fuses tothe conductive layer. The molten "wave" of alkali metal may also contactportions of the upper surface 53 which are not covered by conductivelayer 60, and which are therefore exposed. How ever, as the alkali metalcannot fuse to such exposed portions of upper surface 53, the alkalimetal simply falls off the upper surface 53 to once again expose theupper surface 53.

If the conductive layer 60 is formed from a conductive ink, the layer 60will comprise an exposed surface having metal flecks dispersedthroughout a polymeric material. Since the alkali metal generally fusesto the metallic flecks and not to the polymeric material, the alkali metal may be non-homogeneously distributed superjacent the surface of layer60 when the alkali metal is fused to layer 60. This effect is mitigatedsomewhat by heating the conductive layer 60 during the fusing step. Theheating softens the polymeric material of layer 60, enabling the alkalimetal to penetrate the polymeric material and to thereby fuse with metalflecks that were originally below the exposed surface of layer 60. Theeffect can be mitigated further by plating the conductive layer 60, suchas with the process described previously, so that the exposed surface of60 comprises a uniform metal plate layer. Such a uniform metal platelayer provides an excellent surface for the alkali metal to fuse with.

Generally, if the conductive pad 65 is provided prior to the provisionof anode layer 70, the conductive pad 65 will be covered with a maskinglayer (not shown) during the provision of anode layer 70. This preventsthe alkali metal of anode layer 70 from fusing to either the material ofconductive pad 65 or the material of tip 68 (if tip 68 is present).Preferred masking materials are polyimide or polyester materials, cut toa size which covers pad 65 and leaves layer 60 exposed, and preferablycomprising an adhesive backing to simplify the application of themasking layer over pad 65. An example polyimide material which has beenfound to be particularly satisfactory is a tape sold under the trademarkKAPTON by Dupont.

The provision of anode layer 70 over conductive layer 60 completes theformation of an anode base 71. The individual anode bases 71 can next becut-away and separated from one another. In a less preferred embodimentof the invention, which has not been shown, only one individual anodebase 71 is patterned onto the insulative base 50. In such a lesspreferred embodiment there is no need to cut and separate individualanode bases.

It is noted that the method of formation of anode base 71 of the presentinvention has many steps in common with the above-discussed method offormation of cathode base 31 of the present invention. Accordingly,several of the steps of fabrication of anode base 71 may be donesimultaneously with the steps of fabrication of cathode base 31 . Also,as indicated above, the electrolyte film 40 may be provided superjacentthe anode base 71 instead of, or in addition to, the electrolyte filmbeing provided superjacent cathode base 31.

The alignment and coupling of an anode base 71 and a cathode base 31 toform a battery is next described with reference to FIGS. 4 and 5. Itshould be noted that if a masking layer was provided over conductive pad65, this masking layer will generally be removed prior to the alignmentand coupling of FIGS. 4 and 5 so as to expose the conductive pad 65 andtip 68 (if present).

Referring to FIG. 4, cathode base 31 and anode base 71 are shown afteralignment of anode base 71 with cathode base 31. Note that a slot 15 isaligned with anode contact 67, and that a slot 55 is aligned withcathode contact 27.

The exposed portion of upper surface 11 of cathode base 31 defines anouter area 80 which surrounds the cathode layer 30 and conductive pad25. Also, the exposed portion of upper surface 53 of anode base 71defines an outer area 90 which surrounds the anode layer 70 and thesecond conductive pad 65. Preferably, adhesive is applied over asubstantial portion of one or both of outer areas 80 and 90 prior to thecoupling of bases 31 and 71. The adhesive fastens bases 31 and 71together and also seals the finally formed battery construction. In aless preferable embodiment, adhesive is only applied over the peripheralareas 97 of either or both of bases 31 and 71. (Although the peripheralarea is only shown in relation to base 71, it is to be understood that asimilar peripheral area exists in relation to base 31.) The adhesive maybe applied as a precut film or tape, may be applied before theindividual anode bases 71 are cut-away and separated from one another,and may be cured by heat-sealing.

Referring to FIG. 5, a battery 95 is shown after coupling of bases 31and 71. In the battery construction of FIG. 5, slot 15 allows directselectrical contact to be made with anode 70 through anode contact 67.Also, slot 55 allows directs electrical contact to be made with cathode30 through cathode contact 27. Thus, slots 15 and 55 function as accessports in a battery 95 formed by the method of the present invention.

Another way to look at the battery 95 is that it has a first conductingarea, comprising cathode layer 30 and first conductive layer 20 (shownin FIG. 2F), and a second conducting area, comprising anode layer 70 andsecond conductive layer 60 (shown in FIG. 3E), which are sandwichedbetween nonconductive sheets 10 and 50. Slots 15 and 55 constituteorifices in the nonconductive sheets to provide electrical access to theanode terminal 67 and the cathode terminal 27, respectively.

All of the U.S. patents cited herein are hereby incorporated byreference as if set forth in their entirety.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

I claim:
 1. A battery comprising:a first material; a cathode; and alayer of ink between the cathode and the first material, the ink havinga greater conductivity than the first material.
 2. The battery of claim1 wherein the layer of ink is a cured layer of ink.
 3. The battery ofclaim 1 wherein the cathode is against the layer of ink.
 4. A batterycomprising:an insulative material; a cathode; and a layer of conductiveink between the cathode and the insulative material.
 5. The battery ofclaim 4 wherein the layer of conductive ink is a cured layer ofconductive ink.
 6. The battery of claim 4 wherein the cathode is againstthe layer of conductive ink.
 7. The battery of claim 4 wherein thecathode comprises a cured conductive paste.
 8. The battery of claim 4further comprising:an anode proximate the cathode; an anode terminal inelectrical contact with the anode; an electrolyte film between the anodeand the cathode; and wherein the insulative material is a nonconductivesheet having an orifice therethrough, the anode terminal being exposedfor electrical contact through the orifice.